1. Field of the Invention
The invention relates to a magnetostrictive torque sensor.
2. Description of the Related Art
Known magnetostrictive torque sensors are used on a magnetostrictive rotating shaft with magnetic permeability varying according to applied stress, and are configured such that a variation in magnetic permeability of the rotating shaft when distorted under the applied torque is detected as variation in inductance of a detection coil, thereby detecting a torque applied to the rotating shaft.
When torque is applied to the rotating shaft, compressive (or tensile) stress acts in a direction inclined at a predetermined angle (e.g., +45 degrees) relative to an axial direction and tensile (or compressive) stress acts in a direction inclined at a predetermined angle in the opposite direction (e.g., −45 degrees) relative to the axial direction. Therefore, when the torque sensor is configured that variations in magnetic permeability in the directions inclined at, e.g., +45 degrees and −45 degrees relative to the axial direction are respectively detected by two detection coils and a difference in voltage between two ends is measured on the both detection coils by using a bridge circuit, etc., torque applied to the rotating shaft can be detected at high sensitivity.
Also, a torque sensor has been proposed in which a +45°-detection coil inclined at +45° relative to the axial direction is provided as a first layer, a −45°-detection coil inclined at −45° relative to the axial direction is provided as a second layer, another +45°-detection coil inclined at +45° relative to the axial direction is provided as a third layer, another −45°-detection coil inclined at −45° relative to the axial direction is provided as a fourth layer, and the first to fourth layers are arranged in this order from the rotating shaft side toward the outside (see JP-B-4888015).
In this torque sensor, torque applied to the rotating shaft is measured using a bridge circuit in which the two +45°-detection coils are arranged on a pair of opposite sides and the two −45°-detection coils are arranged on another pair of opposite sides.